1. Field of the Invention
The present invention relates to a transistor having a metal gate electrode formed by using a damascene gate process. In particular, the present invention relates to source and drain electrodes having a low resistance there between.
2. Description of the Related Art
A transistor having a metal gate electrode can be fabricated by using a damascene gate process. Also, a transistor having reduced resistance between source and drain electrodes respectively connected to source and drain impurity diffusion layers can be fabricated by forming nickel silicide on the source and drain impurity diffusion layers.
In the damascene gate process, the source and drain impurity diffusion layers are formed, and thereafter gate insulation film formation and annealing for activation subsequent to ion implantation to a channel portion are conducted. Each of the gate insulation film formation and annealing is a thermal process conducted at a temperature of at least 600° C. However, there is a problem in the use of nickel silicide in that agglomeration is caused by a thermal process conducted at a temperature of at least 500° C. and the resistance between the source and drain electrodes increases to an unacceptable level.